1. Field of the Invention
The invention relates to intake air amount calculating system and method for calculating an intake air amount of an internal combustion engine.
2. Description of the Related Art
An intake air amount calculating system having an air flow meter using a hot wire is known. In this system, electric power supplied to a heating resistor is controlled so as to maintain a constant temperature difference between a resistor for measuring the intake air temperature and the heating resistor. Then, the intake air amount is calculated based on the power supplied to the heating resistor. After start of energization of the heating resistor, it takes some time for the air flow meter to provide desired characteristics. Accordingly, the intake air amount cannot be calculated based on the output of the air flow meter until the desired characteristics are provided.
An intake air amount calculating system having an air flow meter that adopts the micromachine technology is known, as disclosed in, for example, Japanese Patent No. 3475853. In this air flow meter, resistors for measuring the intake air temperature, heating resistors and other components are in the form of thin films. The air flow meter, which uses a microchip device, has a small heat capacity, and can be started up in a short time.
There is also known a system for calculating the amount of air that flows into cylinders, using respective outputs of an intake air temperature sensor, intake manifold air pressure sensor and so forth, as disclosed, for example, in JP-A-5-180057.
When water droplets or ice is deposited on a sensing portion of the air flow meter, however, the air flow meter is not able to accurately calculate the intake air amount even if start-up of the air flow meter is completed.
To calculate the intake air amount with high accuracy, it is essential to correct the intake air amount measured by the air flow meter, based on the intake air temperature. While the air flow meter using the microchip device as described above can be started up in a short time, it takes some time to complete start-up of the intake air temperature sensor. Therefore, even if start-up of the air flow meter is completed, the intake air amount must be corrected based on an estimated intake air temperature until start-up of the intake air temperature sensor is completed, which may result in a situation that the intake air amount cannot be calculated with high accuracy.